Spark plug with a sealing glass mixture with graphite and iron, nickel or cobalt



Dec. 1967 F. ESPER ETAL 3,360,676

SPARK PLUG WITH A SEALING GLASS MIXTURE WITH GRAPHITE AND IRON, NICKEL 0R COBALT Flled June 8 1965 FIG-.3

INVENTORY Fri Z lfi'a/ fr /ermam; FH'

United States Patent Ofiice 3,360,676 Patented Dec. 26, 1967 8 Claims. oi. 313136) ABSTRACT OF THE DISCLOSURE A spark plug having two electrodes with ends located spaced from each other, and an electrically conductive mass located between these two spaced electrode ends in contact with both of the same and consisting of a mass of glass having incorporated therein and distributed therethrough at least partially interconnected particles of graphite and of at least one metal selected from the group consisting of iron, nickel and cobalt.

The present invention relates to a sparkplug electrode arrangement and a method of making the same.

More particularly, the present invention is concerned with the arrangement of the center electrode in the insulating body of a spark plug of the type wherein a center electrode extends through the bore of a tubular insulator, and wherein the center electrode comprises two metallic terminals which are connected by a connector formed of a fused mass of current conducting material, which connector provides a fluid-tight seal in the corresponding portion of the bore of the insulator. One of the metallic terminals may have a collar which abuts against an internal shoulder of the insulator so as to form therewith a seal for pulverulent material, and the connector forms a plug which extends from such shoulder and surrounds the inner end portion of the terminal. This plug contacts the end portions of the two terminals and the wall of the bore so as to form a fluid-tight seal. The terminal formed with the collar may first be inserted into the bore of the insulator, thereafter the fusable pulverulent mixture may be introduced and then the end portion of the second terminal of the electrode, the latter pressing against the pulverulent mixture which thus has been interposed between the two end portions of the terminals within the bore. Upon heating the pulverulent mixture so as to transform the same into a flowable mass, the thus formed fiowable mass will embed the adjacent but spaced end portions of the "two terminals and completely fill the space between the same and the adjacent portion of the wall of the bore in the insulator, thereby forming a fluid-tight seal within the bore.

, It has been proposed to form the plug or connector of pulverulent mixtures which contain copper powder as electrically conductive material since metallic copper is highly conductive and thus, a relatively small proportion of copper in the fused connector or plug will provide the desired high conductivity. However, copper is easily oxidized and it is therefore necessary to include in the plug or seal-forming mixture, for instance, reducing substances in order to prevent oxidation of the copper. To replace copper with silver will considerably increase the costs due to the higher price of this metal. Furthermore, copper as well as silver have relatively high heat expansion coefiicients which are far greater than that of the ceramic material of the insulator and of the glass powder forming part of the mixture which is fused to form the plug or connector. Consequently, upon expansion due to increase in the temperature of the spark plug, and subsequent cooling, the fluid-tight seal might be broken due to shrinking of the plug or connector and this would unduly reduce the useful life span of the spark plug.

It has also been proposed to form the connector or plug in the bore of the insulator of a mixture of glass powder and graphite. However, due to the lesser electric conductivity of graphite, as compared with the conductivity of metals, larger proportions of graphite must be incorporated in the connector in order to obtain the desirable degree of conductivity. Thus, the advantage of lesser heat expansion and absence of oxides due to the reduction of any oxides present under formation of carbon oxide or carbon monoxide which will escape together with entrapped air, is counterbalanced by the lesser mechanical strength of a connector containing graphite as the electrically conductive constituents and, furthermore, particularly at high operating temperatures, connectors formed of graphite-containing fused glass mass do not possess the desired strength.

Furthermore, a connector mass which contains copper as the conductive material will cause formation of a eutectic alloy between the copper of the connector mass and the center electrode terminals if the same consist of silver. Such eutectic alloy frequently will be formed during the fusing of the glass-copper mixture in contact with silver center electrode terminal portions and thereby the end portions of the silver electrode will loose their sharp edge shape and will no longer be firmly anchored within the fused connector mass.

It is therefore an object of the present invention to overcome the above-discussed disadvantages.

It is a further object of the present invention to provide a center electrode assembly for a spark plug and a method of making the same, Which can be simply and economically produced and which will also give good results in cases where the center electrode consists of silver.

It is yet another object of the present invention to provide a center electrode assembly and a method of producing the same, wherein the electrically conductive material of the fused connector mass has a coefficient of thermal expansion which is closer to that of ceramic material and glass than the thermal expansion c-oefiicient of metals such as copper and silver.

Other objects and advantages of the present invention will become apparent from a further reading of the description and of the appended claims.

With the above and other objects in view, the present invention contemplates in a spark plug, a center electrode comprising two metallic terminals having adjacent but spaced end portions, a connector surrounding the end portions and consisting essentially of glass having incorporated therein and distributed therethrough at least partially interconnected particles of graphite and of at least one metal selected from the group consisting of iron, nickel and cobalt, and an insulator having a bore sealingly receiving the connector so that the center electrode and the insulator form an integral unit, the terminals, respectively having second end portions each of which extends beyond one end of the bore.

The present invention also includes a method of assembling the center electrode in the axial bore of an insulator for spark plugs, comprising the steps of inserting one end the end portion remains spaced from the surrounding portion of the insulator, introducing into the bore a pulverulent mixture of glass, carbon and at least one metal selected from the group consisting of iron, nickel and cobalt, so that the pulverulent mixture surrounds the portion of the first terminal and also fills a portion of the bore adjacent to the end portion, introducing into the bore one end portion of a second metallic terminal and maintaining the one end portion of at least one of the terminals in compressive engagement with the pulverulent mixture, heating the pulverulent mixture so as to transform the same into a flowable mass embedding the one end portions of the first and second terminals and simultaneously filling the gap between the insulator and the end portions of the terminals, and allowing the fiowable mass to cool and rigidity thereby forming a rigid connector between the terminals in the bore and fluid-tightly sealing the respective portion of the bore.

' According to the present invention it is proposed that the'connector or plug between the end portions of the terminals of the center electrode within the bore insulator is formed of a pulverulent mixture of a glass powder of preferably substantially even particle size to which as conductive materials a ferrous metal, i.e., either iron, nickel or cobalt powder or a mixture thereof and graphite have been added. In order to achieve high conductivity of the fused connector mass formed upon heating of such pulverulent mixture, it is desirable that the particle size of the electrically conductive pulverulent components is at most only one third of the average particle size of the glass particles. In other words, the glass particles are preferably of substantially even size and at least three times larger than the particles of electrically conductive metal and graphite.

Furthermore, it is advantageous to include in the pulverulent mixture an, adhesive material, preferably dextrin which. will achieve that the electrically conductive pulverulent particles will adhere more or less a coating to the larger glass particles so that after fusing of the mixture the connector will consist of a glass body formed throughout with. a honeycomb structure of electrically conductive material.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however; both as to its construction and its method. of operation, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

FIG. 1 is. an: elevational cross sectional view of a spark plug including the center electrode assembly in accordance with the present invention;

FIG. 2 is a fragmentary section of the end portions of the center electrode terminals within the bore of the insulating body taken along a plane parallel to and spaced from the axis of the spark plug;

FIG. 3 is a greatly enlarged cross sectional view of the pulverulent mixture of which the connector is formed, prior'tofusing of the same; and

FIG. 4 is an enlarged cross sectional view of the mixture of FIG. 3 after fusing of the same.

Refering now to the drawing, and particularly to FIG. 1, spark plug 1 comprises in more or less conventional manner a metallic spark plug housing 2, an insulator or insulating body 3 fluid-tightly fixed in the bore of metallic housing 2 and formed with a longitudinal bore 4. Terminal portion 6 of the center electrode is connected. to a source of electric current and has an end porition located in bore 4 of insulating body 3. Coaxially therewith is arranged the spark forming terminal portions 7 of the center electrode which is also partially located within bore 4 of insulating body 3 and which has a free end extending outwardly from insulating body 3 and coacting with electrode 14 for spark formation. In the interior of the bore 4, a plug of connector 8' is located consisting of a fused mass formed of 70% by volume of glass particles 17% by volume of iron particles 12.5% by volume of graphite and about 0.5% by volume of dextrin, the latter serving as an organic binder which upon mixing of the pulverulent mass will cause coating of glass particles 12 with the conductive iron and graphite particles 13, as shown in FIG. 3. The dextrin is applied preferably with an aqueous solution and will be carbonized during fusing of the mixture.

The center electrode assembly of spark plug 1 is formed in four steps.

At first, silver terminal 7 is inserted through the upper opening of bore 4 and drops through bore 4 until collarshaped portion 9 of silver terminal 7 will come to rest on inner shoulder 10 of bore 4.

Thereafter, an evenly mixed pulverulent mass 8 consisting of the above described mixture of glass, iron, graphite and wetted dextrin, as illustrated in FIG. 3, is introduced into the bore through the upper end thereof. It does not matter if some of the iron particles are somewhat oxidized since the graphite as well as the dextrin constituents of the mixture will act as reducing agents during the fusing of the mixture so that any inadvertently present iron oxide will be converted into metallic iron.

A plurality of the thus formed preassembled spark plug are then heated in a furnace while into each of the preassembled spark plugs a center electrode terminal portion 6 is inserted mechanically into the position illustrated in FIG. 1 so that by insertion of terminal 6 the pulverulent mass 8 will be maintained under pressure while the pulverulent mass is heated to its fusing temperature. The thus produced fiowable mass will yield under the pressure exerted by terminal 6 and will flow about the adjacent end portions of terminals 6 and 7 and will embed the same andv contact the adjacent wall portions of bore 4 so as to form a fluid-tight seal in bore 4. Air, as well as carbon monoxide and carbon dioxide which may be formed by decomposition of dextrin, iron oxide or the like will escape upwardly from the thus formed plug or connector.

Finally, while maintaining pressure, the spark plugs are cooled until the fused connector mass is solidified under formation of a fluid-tight plug 8' surrounding the adjacent end portions of the center electrode and contacting the corresponding portion of the wall of the bore 4. The structure of solidified plug 8 is schematically illustrated in FIG. 4. The individual glass particles 12 have been molten together into a dense glass skeleton 12 which is cross-sected by an interconnected, electrically conductive honeycomb structure 13.

The silver terminal portion 7 of the center electrode which is particularly heat exposed, preferably is formed with a head portion or collar 9 and a projection of cross secting ribs 11 which is partially exposed in FIG. 2 wherein the end portions of the terminal of the center electrode and surrounding structures are shown in a plane parallel to but somewhat forward of the axis of the spark plug. Similarly, part of the end portion of terminal 6, identified by reference numeral 5 is shown in FIG. 2.

Surprisingly it has been found that the center electrode consisting of terminals 6, 7 and connector 8' is of very high electric conductivity namely such that the entire resistance equals only about 10 milliohm plus/ minus 20% which value is nearly the same as that found in spark plugs formed with a connector of glass and copper powder, notwithstanding the fact that theoretically thecopper powder is of much higher conductivity. Without attempting to limit the invention to any specific explanation of the high conductivity of the presently described structure, it may be assumed that the iron particles due to their greater hardness as compared with copper press against each other with greater strength than corresponding copper particles, while the graphite particles, in addition to serving for reducing any oxides and for preventing iron oxide formation, will be embedded more or less in the nature of a packing between the iron and glass components ofthe fused connector. Furthermore, due to their low hardness, the graphite particles may be the reason for the superior crack resistance of the fused connector plug according to the present invention, which is maintained when the spark plug and particularly the end portions of terminals 6 and 7 are exposed to wide temperature fluctuations. Furthermore, the low :heat expansion coefficient of iron, and similarly that of nickel or cobalt will contribute to this unexpected advantage of the structure produced according to the present invention, namely that even upon very severe temperature fluctuations crack formation and thus breaking of the seal or reduction of the electric conductivity are substantially eliminated. Thus, the method of the present invention and the center electrode assembly of the same appear to possess considerable advantages over conventional assemblies of this type, particularly also those which are produced with a fused connector plug consisting of glass and copper.

It is desirable that the mixture of which the connector plug is formed by fusing of the same consists of a major proportion of glass particles, a smaller proportion of metal particles, namely iron, nickel or cobalt or a mixture of the same, a still lesser proportion of carbon and preferably also of a very small proportion of dextrin.

Generally, a glass particles will constitute between 50 and 85% by volume of the pulverulent mixture, iron and/or nickel and/or cobalt particles between and 40% by volume, graphite between 5 and 25% by volume and dextrin between 0 and 2%, most preferably between 0.5 and 1%.

Generally, the graphite particles should be of a size of between 0.1 and 50 microns; preferably about microns, the iron, nickel or cobalt particles of a size of between 1 and 150 microns, preferably about 30 microns, and the glass particles should be of a size at least three times that of the conductive particles and generally between 10 and 500 microns.

The following examples of specific pulverulent mixtures which may be fused to form connector or plug 8' are given as illustrative only, without, however, limiting the invention to the specific details of the examples.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of spark plug diifering from the types described above.

While the invention has been illustrated and described as embodied in a spark plug having two terminals of a center electrode located in a bore of an insulating body and connected by a conductive fused mass, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. In a spark plug, a center electrode comprising two metallic terminals having adjacent =but spaced end portions; a conductive connector surrounding said end portions and consisting essentially of a mass or glass having incorporated therein and distributed therethrough at least partially interconnected particles of graphite and of at least one metal selected from the group consisting of iron, nickel and cobalt; and an insulator having a bore sealingly receiving said connector so that said center electrode and said insulator form an integral unit, said terminals, respectively, having second end portions each of which extends beyond one end of said bore.

2. I a spark plug, a center electrode comprising two metallic terminals having adjacent but spaced end portions; a conductive connector surrounding said end portions and consisting essentially of between 50 and parts by volume of glass having incorporated therein and distributed therethrough at least partially interconnected particles of between 5 and 25 parts by volume of graphite and of between 5 and 40 parts by volume of at least one metal selected from the group consisting of iron, nickel and cobalt; and an insulator having a bore sealingly receiving said connector so that said center electrode and said insulator form an integral unit, said terminals, respectively, having second end portions each of which extends beyond one end of said bore.

3. In a spark plug, a center electrode comprising two metallic terminals having adjacent but spaced end portions; a conductive connector surrounding said end portions and consisting essentially of a mass of glass having incorporated therein and distributed therethrough at least partially interconnected particles of graphite and of iron; and an insulator having a bore sealingly receiving said connector so that said center electrode and said insulator form an integral unit, said terminals, respectively, having second end portions each of which extend beyond one end of said bore.

4. I a spark plug, a center electrode comprising two metallic terminals having adjacent but spaced end portions; a conductive connector surrounding said end portions and consisting essentially of a mass of glass having incorporated therein and distributed therethrough at least partially interconnected particles of graphite and of nickel; and an insulator having a bore sealingly receiving said connector so that said center electrode and said insulator form an integral unit, said terminals, respectively, having second end portions each of which extends beyond one end of said bore.

5. In a spark plug, a center electrode comprising two metallic terminals having adjacent but spaced end portions; a conductive connector surrounding said end portions and consisting essentially of a mass of glass having incorporated therein and distributed therethrough at least partially interconnected particles of graphite and of cobalt; and an insulator having a bore sealingly receiving said connector so that said center electrode and said insulator form an integral unit, said terminals, repectively, having second end portions each of which extends beyond one end of said bore.

6. In a spark plug, a center electrode comprising two metallic terminals having adjacent but spaced end portions; a conductive connector surrounding said end portions and consisting essentially of a mass of glass having incorporated therein and distributed therethrough at least partially interconnected particles of graphite and of iron, nickel and cobalt; and an insulator having a bore sealingly receiving said connector so that said center electrode and said insulator form an integral unit, said terminals,

respectively, having second end portions each of which extends beyond one end of said bore.

' 7; A spark plug as defined in claim 2, wherein said conductive connector consists of between 60 and 78 parts by volume of ,glass, between 9.5 and 21 palts by volume of graphite and between 8 and 26 parts by volume of said at least one metal.

8. A spark plug as defined in claim 7, wherein said graphite particles have a size of between about 0.1 and 50 References Cited UNITED STATES PATENTS 4/1950 Schartzwalder et al; 313\,-136 X 2,505,150 2,837,679 6/1958 Schartzwalder et al. a 2113-136X 3,076,113 1/1963 Candelise 313-136 X 3,247,132

4/1966 Schurecht et al. --313 -,-136 X JAMES w. LAWRENCE, Primary Examiner.

microns, and the particles of said at least one metal have 10 C. R. CAMPBELL, Assistant Examiner.

a size of between about 3 and 167 microns. 

1. IN A SPARK PLUG, A CENTER ELECTRODE COMPRISING TWO METALLIC TERMINALS HAVING ADJACENT BUT SPACED END PORTIONS; A CONDUCTIVE CONNECTOR SURROUNDING SAID END PORTIONS AND CONSISTING ESSENTIALLY OF A MASS OR GLASS HAVING INCORPORATED THEREIN AND DISTRIBUTED THERETHROUGH AT LEAST PARTIALLY INTERCONNECTED PARTICLES BY GRAPHITE AND OF AT LEAST ONE METAL SELECTED FROM THE GROUP CONSISTING OF IRON, NICKEL AND COBALT; AND AN INSULATOR HAVING A BORE SEALINGLY RECEIVING SAID CONNECTOR SO THAT SAID CENTER ELECTRODE AND SAID INSULATOR FORM AN INTEGRAL UNIT, SAID TERMINALS, 